MYCOBACTERIUM AVIUM subspecies PARATUBERCULOSIS causes infectious chronic granulomatous enteritis in ruminants. Calves are most susceptible to infection from birth to a few months of age but the incubation period prior to the onset of clinical signs generally ranges from 2 to 10 years. Fecal-oral transmission from cows to calves is believed to be the most common method of spread; also shed in milk and colostrum. Intrauterine infection can occur but does not appear to be of major importance in the transmission of paratuberculosis. Affected cattle continue to eat even as chronic diarrhea and weight loss persist. In goats the disease primarily affects the upper GI tract and weight loss might be the only obvious sign, with diarrhea intermittent or absent. Usually affects goats 2-years-old or older but yearlings can be affected. Paratuberculosis is common in flocks of sheep but identification of individual sheep with subclinical infections is difficult. Sheep might not show signs for years after being infected and there is often weight loss without other signs.